1. Field of the Invention
The present invention relates to multilayer inductors, and, in particular, to a multilayer inductor preferably for use as an EMI (electromagnetic interference) filter or other suitable filter.
2. Description of the Related Art
Multilayer inductors such as a multilayer inductor 1 shown in FIG. 10 are known. The multilayer inductor 1 is constructed such that an insulation sheet 2b provided with conductive coil patterns 3a to 3e disposed thereon, an insulation sheet 2d provided with conductive coil patterns 4a to 4f disposed thereon, and an insulation sheet 2c provided with a plurality of via holes formed therein are laminated on each other and are sintered integrally with each other to define a multi-layered body. The multilayer inductor 1 shown in FIG. 10 is provided with lead electrodes 5 and 6.
The conductive coil patterns 3a to 3e disposed in the upper portion of the multi-layered body and the conductive coil patterns 4a to 4f disposed in the lower portion of the multi-layered body are each formed in one layer. The conductive coil patterns 3a to 3e and 4a to 4f are electrically connected in series to each other via a plurality of the via holes 8 formed in the insulation sheets 2b and 2c so as to define a spiral coil L. The axis of the spiral coil L is perpendicular to the lamination direction of an insulation sheet 2a and the insulation sheets 2b to 2d and to the extension direction of external input-output electrodes 10 and 11 (see FIG. 11). That is, the axis of the spiral coil L is parallel to the mounting surface of the multilayer inductor 1.
In such a known multilayer inductor, since the conductive coil patterns 3a to 3e disposed in the upper portion of a multi-layered body 9 and the conductive coil patterns 4a to 4f disposed in the lower portion of the multi-layered body 9 are individually formed on the same layers, gaps are formed between the adjacent conductive coil patterns (for example, between the conductive coil patterns 3a and 3b), whereby magnetic fluxes xcfx86 generated by the spiral coil L leak through the gaps.
In order to overcome the problems described above, preferred embodiments of the present invention provide a multilayer inductor in which leakage of magnetic fluxes is prevented and very high inductance is achieved.
According to a preferred embodiment of the present invention, a multilayer inductor includes a multi-layered body including a plurality of insulation layers stacked on each other and laminated together, a plurality of conductive coil patterns disposed in an upper portion of the multi-layered body, a plurality of conductive coil patterns disposed in a lower portion of the multi-layered body, and a plurality of via holes provided in the multi-layered body. The conductive coil patterns disposed in the upper portion and the lower portion of the multi-layered body are electrically connected in series to each other through the via holes so as to define a coil. The axis of the coil is substantially perpendicular to the stacking direction of the insulation layers. Each of the pluralities of conductive coil patterns disposed in the upper portion and the lower portion of the multi-layered body or a plurality of the conductive coil patterns disposed either in the upper portion or in the lower portion of the multi-layered body is formed in and located at different layers. Each conductive coil pattern formed in and located at one of the different layers partially overlaps the conductive coil patterns formed in and located at the other layers.
According to another preferred embodiment of the present invention, a multilayer inductor includes a first insulation layer provided thereon with a plurality of first coil conductors, a second insulation layer provided thereon with a plurality of second coil conductors, a third insulation layer provided thereon with a plurality of third coil conductors, a fourth insulation layer provided thereon with a plurality of fourth coil conductors, and a plurality of via holes for electrically connecting the first, second, third, and fourth coil conductors in series to each other so as to define a coil. A multi-layered body is defined by the first, second, third, and fourth insulation layers which are stacked on each other such that the first and second coil conductors are disposed in an upper portion of the multi-layered body and the third and fourth coil conductors are disposed in a lower portion thereof. The axis of the coil is substantially perpendicular to the lamination direction of the insulation layers, the coil being defined by the coil conductors which are disposed in the upper portion and the lower portion of the multi-layered body and which are electrically connected alternately to each other in series, the second coil conductors overlap gaps formed between each first coil conductor, and the third coil conductors overlap gaps formed between each fourth coil conductor.
In the multilayer inductor according to preferred embodiments of the present invention, each of the pluralities of conductive coil patterns disposed in the upper portion and the lower portion of the multi-layered body or a plurality of the conductive coil patterns disposed in the upper portion or the lower portion of the multi-layered body is formed in and disposed at at least two layers. With this arrangement, gaps formed between each conductive coil pattern disposed in one layer can be covered with the conductive coil patterns disposed in the other layer, whereby leakage of magnetic fluxes can be significantly decreased. In this case, the width of the conductive coil patterns disposed in the outer layer of the at least two layers is preferably greater than the width of the conductive coil patterns disposed in the inner layer.
When at least one nonmagnetic layer is disposed between the different layers provided with the conductive coil patterns, no magnetic paths are provided at the nonmagnetic layer, whereby the leakage of magnetic fluxes is further decreased.
According to various preferred embodiments of the present invention, a multilayer inductor in which leakage of magnetic fluxes is minimized and high inductance is achieved is thus provided.
Other features, elements, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments with reference to the attached drawings.